Pallet loading devices of the general type referred to above are well known in the art. Examples are disclosed in U.S. Pat. Nos. 3,986,621, 3,856,158 and 3,624,782. Conventionally, these devices include an elevator raised and lowered to receive a stack of articles, such as flattened corrugated containers or the like. The operator manually places a predetermined number of articles on a stripping plate which extends over the upper terminus of the elevator's vertical path. As each tier of articles is completed, a switch is actuated to retract the stripping plate, dropping the tier on the elevator bed, if it is the initial tier, and atop the preceeding tier if it is the second or subsequent tier in the stack. The elevator then lowers until the stripping plate path is cleared and, to accommodate the inevitable inertia effect in lowering the elevator, moves upward slightly to return the top of the stack precisely to the stripping plate clearing position. The stripping plate then extends, and the operator places the next tier on the plate. When the selected number of tiers are in place on the stack, the elevator automatically descends to an extreme, lowered position and the stacked load is discharged to a receiving conveyor.
In boxboard plants, depending on the box manufacturing process, flattened boxes may tend to spring open, that is, resist assuming a flattened condition and the tendency to "fluff" or resist formation of a dense stack of boxes will vary with different runs, or orders, of boxes. The boxes are, in the box plant process, stacked into bundles and the bundles are placed on a pallet loading apparatus as described above and assembled into tiers.
Where each bundle or stack is individually strapped before it is tiered in the pallet loading apparatus, the bundles and stack are, of course, quite stable. Where, however, this strapping operation is omitted, the "fluff" or resistance to flattening in the stacked bundle makes the bundle unstable and when it is dropped, by retraction of the stripping plate, onto the underlying bundles, the instability of the load is compounded and toppling of the stack is the likely result, with attendant production delays.
The concept of the present invention alters the operation of the pallet loading apparatus to provide a timed upward movement of the elevator beyond the stripping plate clearing position and after extension of the stripping plate to thereby pack or compress the load on the elevator against the underside of the stripping plate thus eliminating excessive fluff from the stacked load. Stability of the load is greatly increased without the necessity of individually strapping each stack prior to placing it on the pallet loader stripping plate. The time interval during which the additional upward motion of the elevator occurs in adjustable so that the pallet loading apparatus can easily be adapted to provide a uniform desired tightness of the tiers, or stacked bundles, for runs or orders of boxes having differing fluff characteristics upon stacking.